It is typically the goal of electronic reproduction equipment to reproduced sound waves that accurate replicate original sound waves picked up by microphone. Although modern electronic amplifiers that are highly linear across the audible frequency range are now available at low cost, microphones and speakers or headsets differ significantly in their ability to faithfully transform sound waves into electrical signals and back again across the audible spectrum. In addition, room acoustics often cause more degradation in the quality of reproduced sound reproduction than the system components used.
In order to compensate for these and other variations, sound systems commonly include adjustable mechanisms which vary from simple “tone controls” to elaborate “graphical equalizers” that may be manually adjusted by the user to obtain a desired sound quality. In addition, a number of commercially available advanced stereo systems employ automated mechanisms that sample the sound produced by the combination of speakers and room acoustics and then modify relative gain of different channels to compensate for the characteristics of the speakers and the room acoustics. These automated balancing systems are widely used for adjusting the relative magnitude of sound produced by multiple speakers in a “surround sound” system. For example, U.S. Pat. No. 5,666,424 issued to Fosgate et al. on Sep. 9, 1997 describes a surround sound system that employs a microprocessor to digitally control the gain of each channel. The microprocessor receives an input signal from a microphone placed at the preferred listening location within the listening area for automatically balancing the relative channel gains during a calibration process to yield the best possible surround sound reproduction of the stereophonic source material. As a visual aid, the microprocessor displays menus and messages on a video screen, and a visual display shows the relative levels of the six axes of control signals within the surround sound processor.
These automatic calibration systems do not compensate for differences in the hearing abilities of different listeners. Everyone's hearing has a different response to sound. Those with normal healthy hearing perceive sounds at the low and high ends of the audible frequency range at greatly reduced volume. Genetic causes, certain diseases, and exposure to loud noises can further impair hearing in different ways. And as we age, our ability to hear high and low frequencies is reduced even more. The nature and extent of these degradations is different for every individual and, as a result, the sounds we hear, whether “live” or reproduced, are a distorted version of the actual sound pressure waves that reach our ears.
To help restore normal hearing, hearing aids are available that use adjustable filtering and automatic gain control (AGC) parameters. Since given individual's hearing loss is typically not uniform over the entire frequency spectrum of audible sound, with the loss often being greater at higher frequency ranges than at lower frequencies, it has become common for a hearing health professional to make audiological measurements that will indicate the type of correction or assistance that will be the most beneficial to improve that individual's hearing capability.
Various systems for measuring auditory responses are known. These systems usually provide for application of selected tones, broad-band noise, and/or narrow-band noise which is variable in frequency and amplitude to aid in determining the amount of hearing loss a person may have. To assess hearing thresholds for speech, an audiometer may also reproduce live voice or recorded speech at selectable calibrated levels. Various controls are used to administer varying sound conditions to determine a range of responses for the individual. The audiological data which records the individual's hearing response are typically charted or graphed, and these charts are then used as the basis for adjusting the gain vs. frequency characteristics of a programmable hearing aid so that it can better compensate for the hearing loss characteristics of the wearer.
U.S. Pat. No. 5,604,812 issued to Meyer on Feb. 18, 1997 entitled “Programmable hearing aid with automatic adaption to auditory conditions” and the prior art patents cited therein describe hearing aids that can be programmed by the wearer. The hearing-impaired person can retrieve a test program of test tones stored a memory in the hearing aid and can actuate a switch when the desired (appropriate) hearing threshold is reached, and thus store a correction factor each test tone. These stored correction factors adust the signal transfer characteristics of the hearing aid and are retained until the wearer again reprograms the hearing aid in the same way. U.S. Pat. No. 6,035,050 issued to Weinfurtner et al. on Mar. 7, 2000 describes a further “Programmable hearing aid system and method for determining optimum parameter sets in a hearing aid.”